Modern detector systems, such as fire detection systems, intruder detection systems, and flood detection systems include a number of detectors which are connected to a common wired network together with a central control unit. For example, in a fire detection and alarm system, the central control unit, such as a fire alarm control panel (or commonly referred in the art as a Control and Indicating Equipment (CIE)), has a number of detectors connected to it in a loop. The detectors are located throughout a premise to detect changes associated with fire.
As illustrated in FIG. 1, a known fire detection system 10 has a CIE 12, a plurality of detectors, labelled S1 to Sn, and control line 14 connecting, the CIE 12 to the detectors. The control line 14 forms a single loop, beginning and ending at the CIE 12. In this example, the system 10 has only one loop, but it will be appreciated that the system might have a plurality of loops, each loop connecting a plurality of detectors to the CIE 12.
As shown in FIG. 2 another known fire detection system 20 may have one or more CIEs 30, 40, 50 distributed in a monitored area. Referring to FIG. 2, each of the CIEs, for example CIE 30, in the system comprises at least two Input/Output (I/O) terminals 30a, 30b to allow the CIE 30 to be connected, by means of data buses 32, 36 to other CIEs 40, 50 to faint a CIE communication network, so that information from a CIE can be relayed to another CIE through the network. Similarly, each of the CIEs has a plurality of detectors connected to it in a single loop (or multiple loops) as described in the preceding paragraph.
A CIE of the fire detection system of FIGS. 1 and 2 will now be described with respect to FIG. 3.
FIG. 3 shows schematically the components of a CIE 12. In this simplified illustration, the CIE 12 includes a Main Central Processing Unit (MCPU) 60, a Loop Central Processing Unit (LCPU) 62, and a User Interface (UI) 64. For the sake of simplicity, only the MCPU 60, LCPC 62, and the UI 64 are illustrated in FIG. 3. However, it will be appreciated that the CIE 12 may comprise other components, such as memory, or data storage means. By means of an internal bus 66, the MCPU 60, LCPU 62, and the UI 64 are in communication with each other, and other CIEs in the network.
The primary function of the MCPU 60 is to control the overall operation of the CIE 12 including transmitting an alarm signal upon receiving a signal from the LCPU 62 indicating a fire. A plurality of detectors are connected to the LCPU 62 in a single loop so that in event of a fire, a detector can provide an alarm signal to the LCPU 62 which in turn provides a signal to the MCPU 60 so that a decision on what action to take can be made based on a predetermined sequence. Of course, multiple loops of detectors can be connected to the LCPU 62.
The CIE 12 also includes input/output terminals 68, 70 through which data signals can be transmitted to/received from another CIE.
In the prior art, a routing processor is required to route data (or information) between the internal data bus 66 and an external data bus (not shown) in order to transfer data from/to a component of a CIE to another CIE in the network. The routing processor may be incorporated into one of the components of the CIE (for example, the MCPU) to control routing of data between the internal data bus and the external data bus. However, in the event that the routing processor fails, it will not be possible to route the data between the internal bus and the external data bus—resulting in communication failure.